So I've remotely created my first headless using ssh. Now I'm attempting to connect to this VM using RDP so I can install Ubuntu Server, but I cannot get connected at all.

When starting the VM everything appears fine:

$ vboxheadless -s WebTesting
Oracle VM VirtualBox Headless Interface 4.0.16
(C) 2008-2012 Oracle Corporation
All rights reserved.

VRDE server is listening on port 4455.

And showvminfo shows:

VRDE: enabled (Address 0.0.0.0, Ports 4455, MultiConn: off, ReuseSingleConn: off, Authentication type: null)

However I'm still prompted with the "enter your credentials" screen every time I attempt to connect. From reading the documentation null shouldn't prompt me with this screen at all...

Any help with this is greatly appreciated.

P.S. I am using ssh tunneling in putty to tunnel in to my network.